Method of producing electrical sheet steel with cube texture

ABSTRACT

A method for producing double-oriented silicon-iron electrical sheet steel whereby conventional cube-on-edge oriented sheet steel is cross-rolled to about 0.010 inch with at least a 15 percent cold reduction and thereafter annealing the cross-rolled sheet at a temperature within the range 1,950* to 2,250* F. in a hydrogen containing atmosphere having a dew point of -30* F. or less for at least about 5 hours, or for a time sufficient to develop the cube texture.

METHOD OF PRODUCING ELECTRICAL SHEET STEEL WITH CUBE TEXTURE BACKGROUND OF THE INVENTION The grain-oriented electrical sheet steels that are being produced commercially for electrical equipment applications all exhibit a Goss texture (l10)[00l], often referred to as cubeon-edge orientation or single orientation. Because of this preferred orientation, the magnetic properties of such sheet steels are much superior in the direction parallel to the cube edge, i.e., the rolling direction as compared to the transverse direction. This anisotropic characteristic makes such sheet steels ideally suited as a core material for stationary electrical equipment, such as distribution transformers, because the core can be wound parallel to the rolling direction thereby taking full advantage of the superior directional magnetic properties.

The prior art is well aware of the fact that other types of grain-orientation can be produced in electrical sheet steels, for example, the cube texture l)[00l sometimes referred to,,as the cube-on-face orientation or double orientation. In this texture, the cube edges favor orientation parallel to the rolling direction'and also parallel to the transverse direction. With such sheetsteels, therefore, superior magnetic properties exist in both the rolling direction and the transverse direction. Sheet steels having this type of orientation would be very useful in applications such as three-phase transformers and large turbine driven generators in which large amounts of magnetic flux must be controlled in more than one direction.

Intensive eflorts have been made by many investigators duringthe last decade to develop processes for producing electrical sheet steels having the cube texture. Indeed, many patents on such double-oriented sheets and methods of producing it have been developed. However, most, if not all, of these prior art methods are not well suited to commercial produc,ion because of the multiplicity of treatments and difficult stringent con,rols, particularly in the final anneal in which the cubic texture is developed.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a new method for producing the double-oriented or cube texture from a conventional silicon-iron alloy electrical sheet steel, the process having substantially less need for stringent controls to produce a product having an exceedingly high degree of, preferred orientation. In essence, the method involves the cross-rolling of single-oriented sheets, i.e., cube-onedge oriented silicon-iron sheet steels, to a thickness of 0.010 inch or less and then annealing the cross-rolled sheet in a controlled atmosphere at arelatively high temperature to develop a high degree of the double-oriented texture. Of special significance is the fact that the annealing atmosphere may be the same atmosphere used in prior art commercial processes in annealing to produce the cube-on-edge texture.

It is an object of this invention to provide a process for producing silicon-iron electrical sheet steels having a high degree of the double-orientedor cubic texture.

It is another object of this invention to provide a process for producing electrical sheet steels having the double-oriented texture from available silicon-iron electrical sheetsteels having the more conventional single-oriented cube-on-edge texture.

It is a further object of this invention to provide a process for producing electrical sheet steels having the doubleoriented texture without the need. for stringent process controls.

It is still another object of this invention to provide a process for producing electrical sheet steels having the doubleoriented texture by cross-rolling single-oriented silicon-iron electrical sheet steels to 0.010 inch or less and then annealing the cross-rolled sheet at a relatively high temperature to develop the cubic texture, in an atmosphere substantially the same as that used in the production of cube-on-edge sheet.

2 DESCRIPTION OF THE PREFERRED EMBODIMENT As noted above, the process of this invention generally comprises cross-rolling a conventional cube-on'edge oriented silicon-iron electrical sheet steel to a thickness of 0.010 inch or less, and then annealing the cross-rolled sheet at a relatively high temperature, i.e., at least about 1,950 E, to develop the cube-on-face texture, i.e., double-oriented texture.

The starting material may be any of the conventional cubeon-edge oriented silicon-iron electrical sheet steels available commercially. These steels generally have a composition of from 2.50 to 3.50 percent silicon, maximum carbon and sulfur contents of about 0.005 percent and 0.008 percent, respectively, and the other usual impurity elements at conventional residual levels. These sheets are most commonly produced by hot-rolling the alloy to about 0.08 inch, and after cooling and surface cleaning, the sheets are cold-rolled usually to about 0.014 inch or thinner, using a double cold reduction with an intermediate anneal. After the final cold reduction, the sheet is again annealed to decarburize the sheet and to effect a primary recrystallization, and further annealed in a hydrogen atmosphere or a hydrogen containing atmosphere, such as dissociated ammonia, to effect a secondary recrystallization yielding the cube-on-edge texture. Although the above generalized process may be used in manufacturing the cubeon-edge starting material for this invention, it should be understood that any cube-on-edge silicon-iron electrical sheet steel will be suitable for this process by whatever means manufactured, provided however that the carbon and sulfur contents have been reduced to about 0.005 percent and 0.008 percent, respectively, or less during processing. In addition, the cube-on-edge starting material should be relatively free of stringer silica type inclusions that impede grain-boundary mobility, which will therefore impede development of a high degree of orientation in the final cubic texture material as well as the cube-on-edge starting material.

If the starting cube-on-edge sheet is appreciably oxidized or provided with a magnesium-silicate coating, as is the practice in producing such sheet, it will be necessary to remove the coating prior to cross-rolling. To this end, pickling the sheet in a strong acid capable of dissolving the silicate is most suitable. As an example, I have found that pickling the sheet for about 10 minutes in a hydrochloric-nitric acid mixture at room temperature is quite satisfactory. Such pickling will not reduce the sheet thickness by more than about 0.0005 inch.

After the starting sheet steel has been suitably cleaned, and if necessary, cut into suitable lengths for cross-rolling, the individual sheets are cold rolled in a direction perpendicular to the original rolling direction. It is essential that the sheets be reduced to a thickness of 0.010 inch or less, and that the thickness reduction must exceed l5 percent. Although crossrolling reductions somewhat less than 15 percent, followed by a suitable anneal, will produce some degree of cube texture orientation, the extent of this orientation is far below optimum, e.g., on the order of less than about 55 percent of ideal. On the other hand, cross-rolling to more than a 15 percent reduction will greatly optimize cube texture, up to percent of ideal. For the more conventional starting sheets of 0.014 inch, reductions to 0.010 inch should exceed the 15 percent minimum reduction limit, whereas the thicker starting sheets, such as the 0.020 and 0.025 inch will be reduced 50 percent or more in rolling to 0.010 inch, more than sufi'icient to satisfy the minimum limit of 15 percent.

After the sheets have been suitably cross-rolled as described above, they are annealed in a controlled atmosphere above about 1,950 E, for a time sufficient to effect complete recrystallization, both primary and secondary, i.e., at least about 5 hours. Since the sheets are in cut lengths, it is perhaps easiest to box anneal them in a stacked condition. In stacking the individual sheets, they should be dusted with a refractory material, such as granulated alumina, ,that will not contaminate the metal. This will serve to separate the individual sheets apart allowing the annealing atmosphere to penetrate therebetween and prevent the sheets from fusing together.

United States Patent Stanley [45] Feb. 8, 1972 [22] Filed:

[54] METHOD OF PRODUCING ELECTRICAL SHEET STEEL WITH CUBE TEXTURE [72] Inventor: Edward B. Stanley, Washington Township,

Westmoreland County, Pa.

United States Steel Corporation June 25, 1970 [21] Appl. No.: 49,977

[73] Assignee:

[52] U.S.CI. ..148/1ll, 148/112, 148/113 [51] Int. Cl. .110" N16 [58] FieldofSearch ..148/ll0,lll,ll2,113,3l.55

[56] References Cited UNITED STATES PATENTS 3,078,198 2/1963 Wiener ..148/111 3,130,092 4/1964 Kohleretal. ..148/1l1 3,130,093 4/1964 Kohler ....l48/111 3,130,094 4/1964 Kohler et a1. ....148/1 11 3,136,666 6/1964 Taguchi et al. ...,148/l1l 3,163,564 12/1964 Taguchi et a1. ....l48/1l1 3,212,942 10/1965 Takahashi ..l48/1 12 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-G. K. White Attorney-Forest C. Sexton ABSTRACT 3 Claims, No Drawings about 1,950 to about 2,250 E, in a hydrogen containing atmosphere having a dew point no greater than about 30 F., for a time sufficient to develop the cube-on-face orientation.

2. The process of claim 1 in which the annealing time is at least about 5 hours.

3. The process of claim 1 in which the cold rolling effects a reduction of from 15 to 50 percent.

t i 1i l 

2. The process of claim 1 in which the annealing time is at least about 5 hours.
 3. The process of claim 1 in which the cold rolling effects a reduction of from 15 to 50 percent. 